1. Field of the Invention
The present invention is directed towards a sample analyzing system, and more particularly to a system, method and apparatus for injecting reactive species and ions from an ambient ionization source into an atmospheric pressure ion mobility spectrometer.
2. Description of the Related Art
In order to address current and future chemical vapor and aerosol threats to homeland security, chemical detection systems should be versatile and robust to identify hazardous chemicals ranging from traditional chemical warfare agents (CWA) to toxic industrial compounds (TIC). Instruments should operate in an efficient, easy, and safe manner so that trained users can obtain reliable and reproducible readings. Instruments should be flexible to meet changing homeland security goals for chemical analysis, and in particular, have the ability to be portable aiding first responders with the identification of any unknown toxins in the event of a serious industrial accident exposing workers to TICs or public exposure to CWAs from a terrorist attack.
Detection technologies including chemical sensor arrays, electrophoresis-based lab-on-a-chip devices, impedance measurements with modified carbon nanotubes, piezoresistive microcantilevers, and micro gas analyzers have been shown to be potential fieldable technologies capable of chemical agent detection.
Solid phase microextraction (SPME) coupled to gas chromatography (GC), fast GC, and liquid chromatography (LC) are also common approaches to detection of CWAs and TICs in both laboratory and field environments.
Additionally, low ppb detection limits and rapid response of ion mobility spectrometry (IMS) has been shown to be a very useful tool for the detection of CWAs and TICs. Thousands of portable IMS units have been distributed throughout the world associated with aviation security against explosives and battlefield detection of CWAs.
IMS instruments often use a radioactive ionization source (e.g. 63Ni) emitting β-electrons due to its simplicity and reliable performance. However, procedural requirements involving the licensing, placement, use, and disposal of these instruments incur additional costs and regulations. Electrospray, corona and glow discharges, laser, X-ray, and photo ionization techniques are other common ionization techniques used for IMS.
The emergence of new ambient ionization techniques has led to an explosive growth in new applications and methodologies for mass spectrometry (MS) experiments. Largely absent from these advances has been the coupling of ambient ionization techniques to IMS. To date, only the ambient ionization technique desorption electrospray ionization (DESI) has been coupled to reduced pressure IMS for the analysis of pharmaceuticals, peptides, and proteins. One of the primary reasons for this is the difficultly in transporting ambiently-generated ions against an uphill electric field at the entrance of an atmospheric pressure (AP) IMS instrument. Utilization of reduced pressure of ion traps, funnels, or optics to pump ions into the instrument before entering an IM cell within the instrument has been examined.
Known prior art includes US Patent Publications 2008/0173809 to Wu, 2005/0205775 to Bromberg et al., 2008/0121797 to Wu, and U.S. Pat. No. 5,192,865 to Zhu. US Patent Publication 2008/0173809 to Wu discloses that simply placing a plasma ion source in front of the inlet to the ion mobility instrument will be sufficient for efficient ion transmission into the instrument and subsequent ion mobility analysis. However, as one of skill in the art understands, this will only work under two conditions: 1) if the gas velocity flux leaving the ion source is greater than the magnitude of the upfront electric field present at the entrance of the instrument; and/or 2) the ion source is held at a higher floating potential than the entrance electrode of the ion mobility instrument. With one or both of these operating principles, it would be theoretically possible to ionize and effectively transport ions from outside of the entrance electrode of the ion mobility spectrometer to inside it for separation.
Bromberg et al. uses a plasma based ionization technique for ion mobility spectrometry (IMS). Particular mention in Bromberg et al. is spent on the separate placement of an electron beam source, such as a corona discharge, from within the instrument. A window, such as made from diamond or sapphire, allows the electron current to pass into an enclosure region where the sample is held to promote ionization and reduce negative space charging effects.
US Patent Publication No. 2008/0121797 to Wu discloses the use of a sampling substrate, such as a porous media. In 2008/0121797 to Wu, a vapor preconcentrator is used to concentrate desorbed species, which can then be rereleased into an extraction zone for ionization.
Zhu outlines the use of an atmospheric pressure afterglow discharge source coupled to a charged ion detector. However, the implementation as outlined in Zhu focuses on nebulized samples and a solvent return system for sampling in the afterglow region of the source. As outlined in Zhu sampling intact samples could not be possible without interference of the plasma-flux stability since ion/electron charge densities would be in a state of constant flux. Further, the afterglow plasma ion source of Zhu cannot be implemented outside a standalone ion mobility spectrometer since the electric field bias on the ion source would need to be higher than the entrance electrode on the ion mobility spectrometer.
Thus, a need exists for a system using direct in-situ ionization within the electric field gradient of a drift tube (DT) atmospheric pressure IMS instrument to enhance sensitivity, improve ion transport, and provide a safe sampling strategy.